Tsveta Stanimirova

Verified

Tsveta verified their affiliation via an institutional email.

Learn more

Verified

Tsveta verified their affiliation via an institutional email.

Learn more

• PhD
• Professor (Full) at Sofia University "St. Kliment Ohridski"

Clays are essential across industries due to their chemical, mineralogical, and physical properties. They also create favorable conditions for the activation of landslides and soil subsidence during construction activities.. Understanding their characteristics is crucial for improving industrial efficiency and reducing environmental risks. This pap...

A multi-stage DSC-TG approach containing a sequence of dynamic and isothermal modes during heating and cooling in a certain temperature interval was arranged to study the zeolite dehydration/hydration within one experiment. Several parameters related to these processes (such as sample mass changes, dehydration and hydration heats calculated per gra...

This study investigates the mineralogical and geochemical processes of supergene alteration of ore veins in the Hurd Peninsula, Livingston Island. The area, part of the South Shetland Island arc, features hydrothermal veins and supergene zones (enrichment, oxidized, and leached) within the rocks of the Miers Bluff Formation. Fieldwork during the 20...

Weathered granites can contribute to the initiation of natural hazards due to their specific characteristics and response to the environmental conditions. They absorb water during periods of intensive precipitation, and the water saturation further weakens the structural integrity and increases the potential of slope failures and mass movements. Ad...

The ornately illustrated Histoire de l'Art. Le Réalisme. Les Débuts de la Renaissance, Vol. III. Pt. II., publiée sous la direction de André Michel, printed in Paris in 1908, presently a part of the University Library Special Collections, was received in the Conservation Laboratory of Sofia University St. Kliment Ohridski exhibiting signs of deteri...

Acid–base M2+MgAlO and M2+AlO mixed oxides (where M2+ = Mg, Cu, Co, Zn, and Ni) were obtained by thermal decomposition of the corresponding layered double hydroxide (LDH) precursors and used as catalysts for cyclohexanol and benzaldehyde condensation under solvent-free conditions. The catalysts were characterized by X-ray diffraction (XRD), X-ray f...

A theoretical model of the crystal structure of the newly obtained compound Zn4(OH)6SO4·2–2.25H2O based on the compilation of the crystal–chemical properties of two known zinc-hydroxy-sulfate phases—mineral namuwite and hemihydrate—is proposed. The single XRD data confirmed the model and determined the structure, with a trigonal symmetry SG of P-3,...

Hydroxyl sodalite and sulfate cancrinite were synthesized from fly ash from TPP Varna, Bulgaria. The interaction of the two feldspathoids with NH4NO3 solution at 90 °C was investigated. Because of the reaction, sodalite is dissolved and ammonium feldspar (buddingtonite) is formed, which is the first case of low-temperature synthesis of this mineral...

Granular and powdery clinoptilolite tuff samples from Beli Plast, Eastern Rhodopes, Bulgaria, were coated with metal hydroxides (Fe, Al, Fe-Mg) by two-step alkalization. The prepared sorbents were tested for As(III) and As(V) uptake from a modeled water solution with an arsenic concentration of 44 μg/L. The granular sorbent was used in the sorption...

Desorption–sorption processes of clinoptilolite sample from Beli Plast deposit, Bulgaria, were studied in a simultaneous DSC-TG experiment, applying a temperature profile including successive stages of heating up to 300 °C, holding, cooling to 40 °C, holding, and reheating up to 600 °C. Two experiments were provided: in humid static air and dynamic...

The powdered sorbents were applied in a batch system under "static" conditions and showed a much higher adsorption capacity than the granular one. These type of sorbents are more suitable for small quantities of water with a high concentration of arsenic. The possibilities of using all the tested methods for arsenic removal have been evaluated, and...

Clay materials have a variety of unique characteristics and have various applications in many industries. In this paper, we represent new data about the mineralogical and chemical characteristics of the Neogene clay materials from the areas of the villages of Bela and Staropatitsa, Northwest Bulgaria. The phase composition of the samples mainly con...

The possibility of occlusion in melts of useful components of some of the most economically advantageous materials, obtained during zeolitization of fly ash – Na-X, sodalite and cancrinite, was investigated. A very high degree of occlusion of ZnCl2 in zeolite Na-X was achieved along with complete exchange of Na extra framework cations with Zn2+. By...

Quartz, calcite, feldspars, kaolinite, mica (biotite or sericite), and chlorite were determined as predominant minerals. Dolomite, amphibole, and johansenite are presented in smaller quantities. Epidote, hypogene hematite, rarely silver nugget, garnet, rhodonite, and wollastonite are also observed. Pyrite and chalcopyrite, less often sphalerite and...

Experiments with dropwise alkalization of a 0.1 M ZnSO4 solution with 1M NaOH were carried out to establish the formation order of Zn-hydroxy-sulfate minerals (osakaite, namuwite, and lahnsteinite). During the controlled alkalization with 1M NaOH of a 0.1M ZnSO4 solution, namuwite (osakaite), lahnsteinite and wulfingite are successively formed. The...

Osakaite, a new mineral for Bulgaria, was discovered in stalactites from the Gyudyurska mine, South Petrovitsa deposit, South Rhodope. The chemical composition determines isomorphous inclusion of Cu2+ and composition (Zn3Cu)(OH)6(SO4)•5H2O. The mineral is a product of the interaction of mine waters passing through Zn and Cu-sulfide ores. During pro...

Structural characteristics of serpierite samples from Zvezdel, Bulgaria, and Lavrion, Greece, are reported. The thermal behaviour of serpierite from Lavrion is discussed. The chemical composition of the studied samples is analysed by energy-dispersive spectroscopy (EDS) and confirmed by single-crystal structure refinements. The obtained chemical fo...

The Foundation of buildings in soft soil such as quaternary clay is often associated with difficult compaction, settlement, non-uniform and /or excessive deformation, and unsatisfactory shear resistance. The present study aims to assess the possibility of using recycled fines from construction and demolition waste, such as mechanically treated gyps...

The analyzed pottery artifacts derive from vessels from ritual structures and from urns from a necropolis located near the village of Dubene, Karlovo Municipality. The ritual structures are dated to the Early Bronze Age (EBA) III, while the cemetery is dated to the EBA II. All pottery artifacts are studied by optical (petrographic) and XRD analyses...

Foundation of buildings in soft soil such as quaternary clay is often associated with difficult compaction, settlement, non-uniform and/or excessive deformation, and unsatisfactory shear resistance. The present study aims to assess the possibility of using recycled fines from construction and demolition waste, such as mechanically treated gypsum an...

The existence of a specific gallery type of zeolite framework is confirmed. It has been found that similar to HEU-type, STI-type framework can be represented as a layered structure in which two impermeable to water molecules and exchange cations aluminum-silicate layers, separated by diortho-groups, confined gallery-type of porous free space, which...

Cation-exchanged Sr-form of gordaite was successfully obtained from Ca-form of gordaite by an ion-exchange reaction. Data of XRD, SEM-EDS and DTA-TG-MS were used to characterize the Sr-form. Thermal decomposition of Sr-gordaite was studied for the first time in regards of thermal events and mass loss during volatile releasing. It was found similari...

The pre¬sent study shows two mineral types of veins – quartz-polymetallic and quartz-chalcopyrite. The mineral composition of the quartz-polymetallic vein consists of pyrite, sphalerite, chalcopyrite, and galena. The gangue minerals are quartz and chlorite according to optical and XRD analyses. The ore minerals of the quartz-chalcopyrite vein are...

For the first time, a change in the morphology of crystals associated with reversible dehydration processes was revealed and discussed. It was found that in the column of the scanning electron microscope the dehydration proceeds at a high rate and reaches the maximum possible degree that can be achieved at room temperature. The microscopic images s...

Abstract. The studied micas from calc-silicate schists (located in marbles from Dobrostan formation) are members of the calc-silicate mineral association represented by calcite, piemontite, sporadic grains of feldspars (oligoclase/albite), quartz, apatite, zircon, and sphene. The two color types of micas – white to light pale pinkish and green-to-g...

The thermal decomposition process of the ktenasite including different processes such as dehydration, dehydroxylation and evolving of SO2 and O2 is complicated due to the simultaneous presence of both copper and zinc in the system. Dehydration: 1) In the low-temperature interval (20–100 °C) two H2O molecules leave the ktenasite and result in the fo...

The possibilities for ion exchange of new zinc-hydroxy-sulfate-hydrate phase (Zn4(OH)6(SO4)·2.5H2O) were studied. The treatment of the new zinc hydroxy sulfate phase with NaCl results in the formation of gordaite, as the reaction is completed in 72 hours. The behavior of the phase is like that of the mineral namuwite (Zn4(OH)6(SO4).4H2O), which is...

Nunatak de Castillo is situated in the most northeastern part of Hurd Peninsula, Livingston Island, Antarctica. In this area of the island some well exposed small plutonic bodies are cropped out. They are emplaced into the volcanic sequence, known as Mount Bowles Formation. Nunatac de Castillo is a remnant volcanic structure (volcanic plug) with ty...

Published powder diffraction data are analyzed to find the particularities of the aluminosilicate framework and the possible local extra-framework cation-water and water assemblages and their interactions. Contrary to the popular channel model, the porous space in the aluminosilicate framework is examined as a unified, continuous gallery structure...

Rock weathering in high mountain areas at temperate latitudes is considered to be a result of vertical climate zonation interacting with geological structures. In this article, both were taken into account in order to study weathering products in granites in the Pirin Mountain. The whole territory was divided into three geomorphic zones: high-, mid...

A new piemontite occurrence for Bulgaria has been recorded within the calc-silicate schists of the Orelek metamorphic complex. The rock-forming minerals of the piemontite host rocks are represented by enriched by manganese white mica, calcite, quartz, feldspar (oligoclase/albite), and sphene. The pie-montite was characterized in detail by optical i...

Transformation of ktenasite-type minerals (ktenasite and kobyashevite) into langite, posnjakite, and brochantite through leaching of the ion pair (the interlayer M 2+ and the hydroxide layer bonded SO 2− 4) under water treatment was investigated. The observed morphological features of crystals during the transformation suggest a solid-state topotac...

In this paper are presented results from morfological laboratory studies of two representative outcrops in soil in the valey of Duch Kozi Fiiver in the area of Khumbu Himalayas.

A new compound, NaZn4(OH)6(SO4)Br·6H2O named “Br-gordaite”, was obtained by mixing of ZnO with a solution of ZnSO4 and NaBr. The Br⁻ ion occupies the Cl⁻ ion tetrahedral position of the brucite-like layer of the gordaite structure without any other changes relating to the structure and chemical composition. The thermal decomposition of the new phas...

The possibilities of exchange reactions in two types of layer Zn-hydroxy sulfate minerals with neutral and negatively charged hydroxide layer-namuwite (Zn 4 (OH) 6 (SO 4)·4H 2 O) and gordaite (NaZn 4 (OH) 6 (SO 4)Cl·6H 2 O)-were studied. As starting materials, synthetic analogs of these minerals are used. Through direct synthesis, besides the known...

The existing mineralogical classifications are based on the chemical composition with a specification of structural features (Dana and Nickel-Strunz used at www. mindat.org; Kostov, 1993). The anions (monoatomic-halogens, O 2-, S 2-, etc., polyatomic anions-NO 3-, CO 3 2-, SO 4 2-, PO 4 3-, AsO 4 3-, VO 4 3-, etc.) are considered as the main compon...

The hydroxy-salt minerals are normally stable over a small range of external conditions (such as Eh, pH, T, P, concentration of solutions, etc.). Therefore, they are converted easily into each other through changes in the crystal structure. The investigated initial zinc hydroxy salts are characterized by specific layered structures in which the zin...

Combining the processes of freezing and drying by means of adsorption with dehydrated zeolite was proposed as a new auto-freeze drying process. This work describes the changes of temperature and mass of the dried product (car-rot) and of the adsorbent (zeolite Na-A) during the auto-freeze drying process and the influence of different factors on the...

The mixing of dehydrated zeolites with product particles leads to drying of the product, owing to the decrease of relative humidity of the environment and increase the temperature of the mixture, due to the release of adsorption heat. The analysis of the conventional one-stage contact drying process showed a significant mismatching in the water sta...

The dehydration-rehydration processes of three Zn-hydroxy sulfate minerals with interrupted decorated sheet structures – osakaite, gordaite and Ca-gordaite were investigated. The obtained products and processes were characterized by DTA-TG-MS, in situ and ex situ PXRD and FTIR.

The thermal decomposition of three structurally and chemically close compounds: Zn4(OH)6(SO4)·4H2O, NaZn4(OH)6(SO4)Cl·6H2O and CaZn8(OH)12(SO4)2Cl2·9H2O, known as namuwite, gordaite and “Ca-gordaite,” was comparatively studied. The thermal events, the released volatiles and solid residues were studied in the range of 20–1000 °C using TG–DTA-MS and...

The crystal-chemical peculiarities, classification position and nomenclature of the minerals anionic clays were analyzed on the basis of Hawthorne’s binary structural representation – structural unit and interstitial complex (Hawthorne, 1992). The structural units of the anionic clays are presented by positively charged hydroxide layers and as the...

The present study aims to compare mineralogical composition of red soils, formed on marbles in South Bulgaria. We used mineralogical analysis of heavy and light mineral fraction in immersion under polarizing microscope and X-ray diffraction analysis of bulk sample and clay fraction. Three test polygons, located in South Bulgaria were examined: Petr...

The influence of the environment and the weathering conditions on the system parent rock soil is assessed. Three polygons in South Bulgaria, presenting the system parent rock (marbles)-red soil are studied. Chemical and mineralogical compositions of the red soils show that climate and geomorphic positions are as important for the soil-forming proce...

Minerals with the general formula Cu4(OH)6A 2/n n ± pH2O (A = Cl–, NO3–, SO42–) were synthesized and their behaviour following treatment with chloride, nitrate and sulfate solutions was studied by powder XRD and SEM. Two types of transformation were found: (1) an ion-exchange reaction manifested by preservation of both the precursor's morphology an...

The genesis of the products of the alteration of acid pyroclastic material is discussed and interpreted on the basis of the distribution, sedimentation conditions, post-sedimentation activity, mineral and chemical compositions of pyroclastic deposits in Bulgaria and Slovakia. It is found that the disordered nonequilibrium nature of the volcanic gla...

Emanation thermal analysis, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy (SEM) and surface area and porosity determination from nitrogen adsorption/desorption measurements were used to characterize the Mg-Al-CO3 LDH compound with the Mg:Al ratio 3:1 prepared by re-hydration of the Mg-Al mixed oxid...

Emanation thermal analysis, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy (SEM) and surface area and porosity determination from nitrogen adsorption/desorption measurements were used to characterize the Mg-Al-CO3 LDH compound with the Mg:Al ratio 3:1 prepared by re-hydration of the Mg-Al mixed oxid...

Gold is the major ore mineral in Stremtsi occurrence and his alluvial derivates are main object of investigation in the present work. Gold grains were studied by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) to determine their morphological and chemical characteristics. To characterize the environment of local gold depo...

The Layered Double Hydroxides (LDHs) with different cationic composition were obtained by regeneration process of mixed (Mg, Al) oxide (Mg:Al=2:1) with various regenerating solutions. Significant influence of pH on the cation composition of the LDH, obtained during regeneration process was found. The order of cation selectivity at pH 5-6 of regener...

Emanation thermal analysis (ETA) was used to characterize microstructure changes during heating of Mg–Al–CO3 layered double hydroxide (LDH) in the temperature range of 293–1473 K. It was confirmed by ETA that the formation of an intermediate phase with grafted CO32– anions in the hydroxide layers took place in the temperature range of 508–523 K an...

Three series of hydrotalcites (Mg:Al=2:1, 3:1, and 4:1) and their low-temperature intermediate phases were treated with ethylene glycol. The hydrotalcites with 3:1 and 4:1 Mg:Al ratios intercalated ethylene glycol, but the sample with the 2:1 ratio did not. However, a hydrotalcite intermediate phase with carbonate anions grafted into the hydroxide...

A comparative study of the interaction between Ca-Al-Cl, Mg-Al-CO 3 and Ni-Al-CO 3 layered double hydroxides (LDHs) and solutions of Ca 2+ , Mg 2+ , Ni 2+ and Zn 2+ chlorides at 20 and 90 has been accomplished. Possibilities of partial or complete substitution of bivalent cations and a direct comparison of the stability of the investigated LDHs hav...

Enthalpies of hydration of low-temperature hydrotalcite(HT) metaphases have been measured by means of the adiabatic water-vapor absorption calorimeter. The metaphases were characterized by the Mg/Al ratio of 3:1 and CO32- interlayer group. The hydration heat for HT-B (partially dehydroxylated HT with bidentate bonded CO32-) is 2-3 times larger than...

The thermal decomposition of hydrotalcite (HT), with chemical composition Mg1-xAlx(OH)2(CO3)x/2.(1-3x/2)H2O, (0.20 2 in natural and synthetic hydrotalcites (a Mg/Al ratio between 2:1and 3.7:1 ), heated to 800ºC, was investigated by differential thermal analysis, thermogravimetry and evolved gas analysis. At least six endothermic and two exothermic...

The heats of hydration of hydrotalcite (HT) metaphases differing in composition were measured using an adiabatic hydration calorimeter. The metaphase considered in this paper is referred to as HT-B (partially dehydroxylated HT with bidentate-bonded CO32−). Several factors were found to be decisive for the properties of HT-B as a heat adsorbent, nam...

Changes in cation composition and M2+/M3+ ratio during hydrotalcite regeneration were studied. Regenerated hydrotalcites were obtained by recrystallization of mixed (Mg, Al) oxides in solutions of divalent (Mg, Zn, Co, Ni, Cu) or trivalent (Al, Fe) cations.Heating Mg–Al–CO3 hydrotalcites with Mg/Al=2, 3 and 3.7, at 600 °C for 2 h yielded periclase-...

Ni-Al takovite-like systems with Ni2+/AI3+ ratios of 0.5 (Ni-poor) and 2.8 (Ni-rich) have been synthesized and modified by introducing Cr3+ ions into the structure. Two procedures of precipitation at pH 8 from the aqueous solutions of the nitrate salts of the elements (coprecipitation of all the components and separate precipitation) were used to i...

Ni-Al takovite-like systems with Ni2+/AI3+ ratios of 0.5 (Ni-poor) and 2.8 (Ni-rich) have been synthesized and modified by introducing Cr3+ ions into the structure. Two procedures of precipitation at pH 8 from the aqueous solutions of the nitrate salts of the elements (coprecipitation of all the components and separate precipitation) were used to i...

The calcian crypto-to microcrystalline dolomites (Mogila Formation) originated in a mild arid peritidal depositional environment through complete early diagenetic replacement of lime sediments, at low Mg/Ca ratio of the dolomitizing fluids and salinity closer to normal marine water. The preservation of their non-stoichiometry was mainly controlled...

A hydrotalcite specimen from the Snarum deposit (Norway) is investigated. Three morphological varieties of hydrotalcite are established whereupon the 2H, 3R and 6R polytypi modifications are obtained. The 6R polytype is established for the first time in the Snarum deposit. A method to check and specify the indexing by means ol computer subtraction...

The regeneration of the high-temperature metaphase (HT-P) in hydrotalcite was examined. It was found that the process takes place through crystallization from solution. The only observed indication for the "memory effect" is the preservation of the Mg/Al ratio of the initial sample in the regenerated samples.

Synthetic hydrotalcite-like samples with composition [M1 – x 2+Alx 3+(OH)2](CO3)x/2 nH2O, where M = Mg, Ni, x = 0.25 and 0.33, n = 2x and 1.5x, are studied by XRD, DTA, TG and IR spectroscopy after heating in the temperature interval 120–260 C and rehydration in air and water. Structural models of the two metaphases obtained are proposed. Metahydro...